This invention relates to a differential thermal analyzer or calorimeter and, more particularly, to a differential thermal analyzer of a heat flow type using a thermoelectric disc to transfer heat to the sample.
There are many differential thermal analyzers available on the market today. Most of these analyzers utilize a heated block with sample and reference specimen capsules. The differential temperature changes that the sample undergoes relative to the reference material is used as an indication of the thermal properties of the sample under test.
One of the thermal analyzers presently available for effecting this test utilizes a thermoelectric disc made of constantan. The disc serves as a thermally conductive path for heat transfer to and from the sample. In addition, the disc serves as or provides a part of one of the differential temperature measuring thermocouples. Typically, the disc is firmly attached to a silver, programmed temperature surface and two symmetrically positioned, raised platforms serve as the sample and reference material holders. A chromel wire is connected to each platform to form a chromel-constantan differential temperature monitoring thermocouple. A purge gas is passed through the cell. An alumel wire is affixed also to the sample platform contiguous the chromel wire to provide a sample temperature sensing thermocouple. The outputs of the thermocouples are coupled to conventional amplifiers and eventually applied to an XY recorder wherein the differential temperature between the sample and the reference material is recorded on the Y axis and the temperature of the sample is recorded on the X axis.
While these thermal analyzers of the prior art are generally satisfactory, they suffer from the disadvantage of being sensitive to the placement or positioning of the sample material holder and the reference material holder (on the raised platform). Since the temperature of the sample and reference material is sensed from a point source, if the sample and reference holders or the thermocouple junctions are misplaced or mispositioned to any degree, the various runs are not reproducible and, in fact, not representative of the true thermal properties of the sample.
Accordingly, it is an object of this invention to obviate many of the disadvantages of these prior art thermal analyzers.
A further object of this invention is to provide an improved thermal analyzer that is capable of providing more reproducible results.